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Partial projective representations and partial actions. (English) Zbl 1211.20016
The purpose of the present article is to define partial projective representations of groups in analogy with the classical representation theory. This notion is closely connected with the notions twisted partial products and twisted partial actions [see M. Dokuchaev, R. Exel and J. J. Simón, J. Algebra 320, No. 8, 3278-3310 (2008; Zbl 1160.16016)].
First, the authors give the necessary information about projective representations of semigroups and their factor sets [see B. V. Novikov, Dopov. Akad. Nauk Ukr. RSR, Ser. A 1979, 472-475 (1979; Zbl 0411.20047)]. After that they define equivalent factor sets, product of factor sets and Schur multiplier of a semigroup with identity. So the authors define partial projective representations of a group by means of projective representations of a semigroup which is associated with the group. It is given another definition, which is independent of semigroups. Later in the paper is studied the structure of the factor sets of partial projective representations. The connections between the projective partial representations and the twisted partial actions are also investigated.

##### MSC:
 20C25 Projective representations and multipliers 20M30 Representation of semigroups; actions of semigroups on sets 16S35 Twisted and skew group rings, crossed products
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##### References:
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